Long-chain fatty acids are essential components of membrane lipids and play and important role in energy metabolism of the cell. Palmitate, the most abundant fatty acids, is synthesized through a de novo pathway through head-to-tail condensation of the C2 units. The enzymes systems involved are the acetyl-CoA carboxylase and the fatty acid synthase. Recent advances in studies of the mechanism, structure-function relations, and cloning of these enzymes make it possible and timely to investigate the regulation of the genes coding for these multifunctional enzymes. The yeast, Saccharomyces cerevisiae, will be used in the proposed studies. In this organism, the carboxylase is a homotetramer of a subunit molecular weight of 250,000, while the fatty acid synthase consists of two subunits alpha (M, 207,000), that are organized in an alpha6beta6 complex. The genes FAS2, FAS1, and FAS3 code for alpha, beta, and carboxylase subunits, respectively. These enzymes are subject to regulation of exogenous fatty acids. When yeast is grown in the presence of fatty acids, these genes are regulated. Acyl-CoA derivatives of long and intermediate chain length act as corepressors. Through mutational analyses of the cloned genes, the regulatory regions of these genes will be identified. Isolation of regulatory factors and characterization of the corepressor will help us understand the fatty-acid-mediated repression of these genes.